A known conventional configuration (e.g., patent document 1) of a vehicle seat is such that a single synthetic resin plate capable of supporting the back of a seated passenger is attached to a seat back frame for a seat back via wire springs so as to freely move forward or backward relative to the seat back frame.
Another known conventional configuration (e.g., patent document 2) of a vehicle seat is such that an internal structure in the form of a quadrangular frame is fixed to a seat back frame, sideways elastic bending parts are attached to the left and right sides of the internal structure, a spring plate is disposed between the elastic bending parts, and lumbar supports are disposed on the upper and lower sides of the spring plate via a vertical elastic bending part.
Another known conventional configuration (e.g., patent document 3) of a vehicle seat is such that a single synthetic resin plate capable of supporting the back of a seated passenger is fixed to a seat back frame via wire springs so as to freely move forward or backward, an adjusting part movable forward or backward is disposed on part of the plate, thereby adjusting the elastic force for supporting the body of a seated passenger.
Patent document 1: JP 2006-21716 A
Patent document 2: JP 11-206506 A
Patent document 3: JP 2006-111066 A